Question

A car sounding its horn at $480Hz$ moves towards a high wall at a speed of $20m{s}^{-1}$ . If the speed of sound is $340m{s}^{-1}$ , the frequency of the reflected sound heard by the girl sitting in the car will be closest to

• A. 540 Hz
• B. 524 Hz
• C. 568 Hz
• D. 480 Hz

Answer 1

Answer: (A)

The frequency of reflected sound heard by the girl,
$n^{{}^{\prime }}=n\left[\frac{v-\left(-v_o\right)}{v-v_s}\right]=n\left[\frac{v+v_o}{v-v_s}\right]$
$=480\left[\frac{340+20}{340-20}\right]=540Hz$